1. Field of the Invention
The present invention generally relates to radio frequency switches and, more particularly, to a microelectronic mechanical system switch that is less susceptible to mechanical malfunction due to stiction effects.
2. Description of the Related Art
Radio frequency (RF) switches are widely used in microwave and millimeter wave integrated circuits (MMICs) for many antenna applications including phased arrays. In general, such applications rely on semiconductor solid state switches, such as GaAs MESFETs and PIN diodes. When the signal frequency exceeds about 1 GHz, solid state switches suffer from large insertion loss in the xe2x80x9cOnxe2x80x9d state (i.e., closed circuit) and poor electrical isolation in the xe2x80x9cOffxe2x80x9d state (i.e., open circuit). Microelectronic mechanical system (MEMS) switches have distinct advantages over solid-state devices in all these characteristics, particularly above 1 GHz. MEMS technology is a process for fabricating components of an electronic circuit using micromachining.
In general, MEMS switches are susceptible to a phenomena known in the art as xe2x80x9cstictionxe2x80x9d. Stiction generally occurs when attracting forces between contacting surfaces overpower the restoring force of the switching element. Stiction is variously attributed to micro-welding of metal species between contacts, build-up of non-metallic microcontaminates such as organic compounds between contacts, and electrostatic charge build-up on nearby or contacting dielectric materials. Stiction can cause the switch to malfunction by permanently sticking in the xe2x80x9conxe2x80x9d position. It can also result in delayed switching and poor isolation in the xe2x80x9coffxe2x80x9d state.
Therefore, there exists a need in the art for a MEMS switch that is less susceptible to mechanical malfunction due to stiction effects.
The disadvantages associated with the prior art are overcome by a microelectronic mechanical system (MEMS) switch comprising a relatively inflexible vane and flexible hinges formed over a substrate for electrically coupling an input line to an output line formed on the substrate. The flexible hinges support the vane above the input line so as to define a pivot axis that is parallel to the substrate. The vane and hinges are actuated by pull-down and pull-back electrodes formed on the substrate. Specifically, when a predetermined DC voltage is applied to the pull-down electrode, electrostatic forces between the vane and the pull-down electrode pull the far end of the vane onto the output line, pull the middle of the vane onto the fulcrum, and flex the hinges. The DC voltage is subsequently removed from the pull-down electrode and a predetermined DC voltage is applied to the pull-back electrode. Electrostatic forces between the vane and the pull-back electrode pull the near end of the vane toward the pulldown electrode, and since the middle of the vane is on the fulcrum, the far end of the vane is levered off the contact. In the present invention, the force provided by the pull-back electrode acts in concert with the restoring force provided by the de-flexing of the hinges.